How do I use yum command to update and patch my Red hat Enterprise Linux / CentOS Linux version 5.x server via RHN / Internet? Can I use up2date command under RHEL 5?
up2date command was part of RHEL v4.x or older version. You need to use yum command to update and patch the system using RHN or Internet. Use yum command to install critical and non-critical security updates as well as binary packages. Login as the root user to install and update the system.

Task: Register my system with RHN

To register your system with RHN type the following command and just follow on screen instructions (CentOS user skip to next step):# rhn_register

WARNING! These examples only works with RHEL / CentOS Linux version 5.x or above. For RHEL 4.x and older version use up2date command.

Task: Display list of updated software (security fix)

Type the following command at shell prompt:# yum list updates

Task: Patch up system by applying all updates

To download and install all updates type the following command:# yum update